Hey there sorry that it took me a little while to reply.
The Whole Story...:-)
We bought the house about 3 weeks ago; this is our first house with a pool.
There is an inside controller in the kitchen, the Jandy RS8. There is also an outside controller mounted on the coping of the spa. Both of these worked until last week. The big control unit is mounted on the wall by the pumps.
Last week I noticed that the inside controller was displaying "5250 rev C", and seemed unresponsive. I started digging around the Internet trying to find a solution, and then pushed the reset button on the side of the controller. The message changed to "6700 rev C". When I talked to my wife about it, she said that the spa controller was "flashing and acting crazy." Indeed, it's flashing nonsense characters.
When I got your reply, I went out to the master unit and removed the cover panel. The brown bus to which you refer (directly to the right of the 4-wire 'red plug', and is labeled on the wiring diagram inside the cover as "spa controller" (or something like it) has nothing attached to it.
The inside controller occasionally will work (generally in the evenings, although that may be a coincidence). It acts completely normally and I can control all the features with it. Then it'll error out again and be unusable. I can't find any causal relationship between it working and not working.
However, working or not, the spa-side unit continues to either be totally dead-looking or flash gibberish.
Everything works from the master controller when I put it in "service" mode.
I hope this helps light the way a little more, and thanks!